Inkjet recording apparatuses are popularly used for printers, facsimiles, copiers and multifunctional machines including functions of printer, facsimile and copier. An inkjet recording apparatus, for example, forms an image on a sheet using a recording head or an image forming mechanism equipped with a liquid droplet ejecting head for forcing “ink droplets” of a recording liquid (hereinafter referred to as ink droplets) out to adhere the ink droplets to the sheet while conveying the sheet. Thereby, image formation is carried out. The term “sheet” as used herein not only refers to a paper sheet, but also refers to a recording medium, a transfer material, a recording sheet and the like. The term “image formation” as used herein refers to recording, printing and imaging.
An image forming apparatus can form images on any of various materials as the recording medium, such as paper, thread, fiber, cloth, leather, metal, plastics, glass, wood, and ceramics, by ejecting ink droplets. The term “image formation” as used herein not only refers to forming an image with meanings, such as characters or figures on a recording medium, but also refers to formation of an image without meanings such as patterns. The term “liquid” as used herein is not limited to a recording liquid or an ink, but any kinds of fluids that can be ejected can also be used.
In a case where an image is formed by an inkjet recording method, ink is adhered to a sheet. Consequently, the moisture contained in the ink causes the sheet to deform. This phenomenon is referred to as cockling. Due to cockling, the sheet may ripple so that the position of a nozzle of the recording head and the sheet surface varies from place to place. In a case where the level of cockling is high, in a worst case, the sheet touches the nozzle surface of the head, thereby contaminating the nozzle surface of the head and the sheet itself. As a result, the image quality deteriorates, and a misalignment of the ink droplet landing position may occur due to an effect of cockling.
In view of the above, in a related art inkjet recording apparatus, for example, an endless charging belt to maintain the flatness of a sheet is often provided. The charging belt surface is charged so as to electrostatically suction the sheet. By forcing the charging belt to circulate in this state and to convey the sheet, the sheet is prevented from separating from the charging belt (i.e. the sheet is prevented from rippling). Accordingly, the sheet can maintain a high degree of flatness.
Since cockling and curling of a printing sheet affect printing image, in a related art printing sheet conveyance apparatus for carrying out a printing operation in which a printing sheet is electrostatically suctioned by an electrostatic suction member at a printing position to print on the printing sheet and for moving printing sheet, a mechanism for switching, depending on a type of printing sheet used, between a state where the printing sheet is suctioned by the electrostatic suction member and a state where the printing sheet is not suctioned by the electrostatic suction member is proposed.